1. Field of the Invention
The present invention relates to a self-propelled working machine, such as a lawn mower, that performs work by using power of an internal combustion engine and travels by using power of an electric motor, and more particularly, to a self-propelled working machine of which travel is controlled in response to working load.
2. Description of the Related Art
In self-propelled working machines, in general, working load increases when travel speed is high during the working, and working load decreases when travel speed is low.
In such self-propelled working machines that perform work by using an internal combustion engine, if working conditions are bad and working load is too large, it is not possible to perform the work at optimum output and the finish of the work deteriorates, or engine stall occurs. For this reason, the operator determines the degree of the working load by hearing working sounds or observing the finish. When it is determined that the working load is increased, the operator reduces the travel speed and thus suppress the load to maintain excellent finish of the work so that the internal combustion engine does not stop running (engine stall does not occur).
As described above, the operator must control the speed while observing working conditions. For this reason, operator's work burden is increased. Therefore, the operator should have proficiency in operating the working machine.
There has been proposed a snowplow in JP-UM-A-3-32617. In the snowplow, a blower and an auger are driven to remove snow by an internal combustion engine and the snowplow travels by the internal combustion engine. The travel speed of the snowplow is controlled and the rotational speed of the blower is also controlled in response to working load.
According to the snowplow disclosed in JP-UM-B-3-32617, one internal combustion engine performs the drive of the blower plow and so one, and the engine rotational speed of the engine has an influence on the travel speed. Further, since the blower and wheels are two objects to be controlled, the snowplow includes separate control actuators for these objects. For this reason, the structure of the snowplow including the driving mechanisms is complicated, and the control thereof is complex, thereby increasing the overall cost.